Dipstick assay to identify leprosy patients who have an increased risk of relapse

Classification of leprosy patients into paucibacillary (PB) and multibacillary (MB) determines the duration of treatment; misclassification increases the risk of relapse because of insufficient treatment if an MB patient is classified as PB. We explored the possibility of using a simple dipstick assay based on the detection of antibodies to the Mycobacterium leprae-specific phenolic glycolipid-I (PGL-I) as a tool for classification of patients into PB and MB for treatment purposes. The sensitivity of the dipstick test for detection of MB patients was 85.1%, the specificity 77.7%. We found that of the 71 dipstick negative PB patients 25 (35.2%) were clinically cured at the end of treatment, compared with only two (9.5%) of the 21 dipstick positive PB patients. Of 170 patients in the study population, nine (5.3%) relapsed within the 5-year follow-up period. Seven were MB patients, all dipstick positive. Two PB patients relapsed, one was dipstick negative and one was dipstick positive. Dipstick positivity is a risk factor for the future development of relapses, especially in those groups of patients who had received a shorter-than-usual course of treatment and the dipstick can be used as an additional, simple tool for classification of patients and for identification of those patients who have an increased risk of relapse.